The effect of pH on the synthesis of reduced graphene oxide (RGO)-CdS nanocomposites via a hydrothermal method was investigated. Higher pH is more favorable for the formation of good quality RGO-CdS nanocomposites. The photocatalytic performance of the composites was investigated by measuring the reduction of Cr(VI), and the composite synthesized at high pH (=11) exhibited a 76% removal rate of Cr(VI). At high pH, the development of CdS particles of smaller sizes and the maximum number of Tr-electrons available in RGO increased the effective surface area available for light absorption, fast electron transport, and enhanced light absorption intensity. The staircase band structure of CdS in combination with RGO helped to inhibit electron-hole recombination, which enhanced photocatalytic activity. (C) 2014 Elsevier B.V. All rights reserved.